Speckle photography of lateral sinusoidal vibrations: error due to varying halo intensity

The effect of varying halo intensity in speckle photography of lateral sinusoidal vibration using Young's fringes is discussed. An interesting new result is found that, for nonunity contrast or visibility, the relative fringe shift (or the error) for minima is always minimum for the lower-order fringes. Also the error in the fringe maxima position is lowest generally at intermediate fringe orders. However, as the visibility reduces the trend becomes similar to that for the case of minima. For maxima and minima both, the error is less for larger amplitude vibrations and higher visibility.